Possible latitudinal clines in Antarctic intertidal and subtidal zone communities encrusting ephemeral hard substrata

Aim Encrusting faunal communities on rocks were examined from Southern Ocean intertidal and subtidal (6 m) zones to investigate potential change with latitude. Location The site locations were South Georgia (54°S [sub-Antarctic]), Signy Island (60.5°S [maritime Antarctic]) and Adelaide Island (68°S [high Antarctic]). Methods The number of taxa, degree of colonization and bryozoan growth and mortality were measured. Results The communities present were relatively simple in terms of composition and interactions. Spirorbid polychaetes (Annelida) and cheilostomatid bryozoans were the principal components. The community simplicity and dominance of unitary (compared to colonial) fauna increased with latitude. Mean annual mortality of subtidal cheilostomatids also significantly increased with latitude. The number of bryozoan species and potential aspects of community complexity increased with latitude. The growth of the bryozoan Inversiula nutrix increased with latitude reversing the general trend of decreased growth rate. Conclusions These findings suggest that disturbance may significantly increase with latitude within the Southern Ocean. The apparent reversal of typical latitudinal growth trends is probably a result of classical island biogeography, with species decreasing away from a centre of high diversity.     

Predation by Patiria miniata (Asteroidea) on bryozoans: Prey diversity may depend on the mechanism of succession

Summary In environments where frequent disturbances interrupt the successional process there will usually be many patches of habitat at intermediate stages of succession. It is then relevant to consider the factors which control local diversity during succession. In offshore kelp forests across the whole Southern Californian Bight settlement panels were rapidly colonised by two species of cyclostome bryozoans (Tubulipora tuba and T. pacifica); but cheilostome bryozoans eventually became dominant during succession because they were able to grow over Tubulipora spp. When abundant, Tubulipora spp. were apparently able to reduce the number of colonies, and hence the number of species, of cheilostome bryozoans settling on the panels. Thus the rapid colonisers may delay the process of succession and reduce the diversity of bryozoans during succession. In field and laboratory experiments we found that the asteroid Patiria miniata preys on Tubulipora spp. but not on cheilostome bryozoans. The predator speeds up the successional process and increases bryozoan diversity by reducing the cover of Tubulipora spp. Other ways in which predators may influence diversity during succession are discussed. The effect of predation may depend on the abundance of the prey and the mechanism of succession.     

Bryozoan populations reflect nutrient enrichment and productivity gradients in rivers

1. The hypothesis that nutrient enrichment will affect bryozoan abundance was tested using two complementary investigations; a field‐based method determining bryozoan abundance in 20 rivers of different nutrient concentrations by deploying statoblast (dormant propagule) traps and an experimental laboratory microcosm study measuring bryozoan growth and mortality. These two methods confirmed independently that increased nutrient concentrations in water promote increases in the biomass of freshwater bryozoans. 2. Statoblasts of the genus Plumatella were recorded in all rivers, regardless of nutrient concentrations, demonstrating that freshwater bryozoans are widespread. Concentrations of Plumatella statoblasts were high in rivers with high nutrient concentrations relative to those with low to moderate nutrient concentrations. Regression analyses indicated that phosphorus concentrations, in particular, significantly influenced statoblast concentrations. 3. Concentrations of Lophopus crystallinus statoblasts were also higher in sites characterised by high nutrient concentrations. Logistic regression analysis revealed that the presence of L. crystallinus statoblasts was significantly associated with decreasing altitude and increasing phosphorus concentrations. This apparently rare species was found in nine rivers (out of 20), seven of which were new sites for L. crystallinus. 4. Growth rates of Fredericella sultana in laboratory microcosms increased with increasing nutrient concentration and high mortality rates were associated with low nutrient concentrations. 5. Our results indicate that bryozoans respond to increasing nutrient concentrations by increased growth, resulting in higher biomasses in enriched waters. We also found that an important component of bryozoan diets can derive from food items lacking chlorophyll a. Finally, bryozoans may be used as independent proxies for inferring trophic conditions, a feature that may be especially valuable in reconstructing historical environments by assessing the abundance of statoblasts in sediment cores.     

A new encrusting interstitial marine fauna from Brazil

Abstract. This paper reports the second occurrence of a sand‐grain encrusting interstitial epifauna dominated by bryozoans and polychaetes at a site thousands of kilometers from the first described occurrence of such a fauna 20 years ago. Such faunas seem to have gone almost unrecorded in the marine ecological literature, but they are potentially geographically widespread and ecologically significant, deserving recognition and further study by benthic ecologists. Although rooted‐erect and free‐living lunulitiform bryozoans can be abundant in soft‐bottom habitats, the presence of encrusting forms was, until recently, considered to be limited to patches of hard substrata. In 1985 and 1988, a new and seemingly unique habitat for encrusting bryozoans and other organisms on single grains of shell or sand was reported from the coastal waters of Florida, USA. Here we report a second discovery of an interstitial encrusting fauna from the continental shelf off the state of São Paulo, Brazil. In addition to the cupuladriid Discoporella umbellata, several species of bryozoans (9 cheilostomes, 3 ctenostomes, and 1 cyclostome) were found encrusting on or boring into sand grains from the 4 stations examined. Four species were found exclusively on sand to gravel size grains. The most abundant colonies, with ～1300–1500 colonies m^?2, belonged to a new species of Cleidochasma. New species of Trypostega and Reginella, each with up to 200–300 colonies m^?2, were also discovered. The grain‐encrusting bryozoans were characterized by their small size, and by the fact that sexual reproduction was initiated very early in colony growth; brood chambers (for the development of embryos into larvae) occurred in colonies having only a few zooids. Colonies of boring ctenostome and cheilostome bryozoans were even more abundant than those of grain encrusting forms, being present in almost every piece of shell (～5000–5500 colonies m^?2). The fauna also included representatives of other groups of encrusting organisms, especially tubeworms (11,000–13,000 tubes m^?2). Planned work on samples from additional stations on the São Paulo shelf will no doubt yield a larger number of species from various taxa and perhaps show some overlap in sand fauna species between the Brazilian and Floridian sites. In addition to the unique species of single grain encrusters, colonies of bryozoan species characteristic of larger subtidal hard substrata were also found on sand or gravel size grains, indicating that an interstitial refuge may be available to some epifaunal taxa and suggesting that this interstitial refuge, which remains almost completely unknown to benthic ecologists, may play a large role in determining distributions of those taxa.     

新疆西准噶尔晚泥盆世法门期的苔藓虫动物群及其形态特异性和古环境意义*

本文重新研究了产自新疆西准噶尔晚泥盆世法门期洪古勒楞组和铁列克提组的苔藓虫动物群, 重点关注其形态学特征和古生态学意义。该苔藓虫动物群由隐口目(Cryptostomata)、窗格苔藓虫目(Fenestrata), 变口目 (Trepostomata)和泡孔目(Cystoporata)组成。优势类群隐口目苔藓虫是具有中轴或中板的细枝状和双叶状群体。 它们的虫室具有加厚的外区体壁, 弯曲强烈的自虫室, 数量众多的大虫室(metazooecia)或隐蔽虫室(tectizooecia), 以及径向刺突和/或棘状刺突。多样化的异虫室、刺突、自虫室等结构, 以及不同生长环境中的不同生态组合是新疆西准噶尔法门期苔藓虫成功演化的基础。洪古勒楞组下段和铁列克提组下部的苔藓虫动物群可以划分为三类生态组合(即: No. 1, No. 2和No. 3), 代表前滨—近岸—远岸的沉积环境。其中, 近岸环境的枝状—双叶状—网状苔藓虫组合的属种丰度、分异度最高。     

新疆西准噶尔晚泥盆世法门期的苔藓虫动物群及其形态特异性和古环境意义*

本文重新研究了产自新疆西准噶尔晚泥盆世法门期洪古勒楞组和铁列克提组的苔藓虫动物群, 重点关注其形态学特征和古生态学意义。该苔藓虫动物群由隐口目(Cryptostomata)、窗格苔藓虫目(Fenestrata), 变口目 (Trepostomata)和泡孔目(Cystoporata)组成。优势类群隐口目苔藓虫是具有中轴或中板的细枝状和双叶状群体。 它们的虫室具有加厚的外区体壁, 弯曲强烈的自虫室, 数量众多的大虫室(metazooecia)或隐蔽虫室(tectizooecia), 以及径向刺突和/或棘状刺突。多样化的异虫室、刺突、自虫室等结构, 以及不同生长环境中的不同生态组合是新疆西准噶尔法门期苔藓虫成功演化的基础。洪古勒楞组下段和铁列克提组下部的苔藓虫动物群可以划分为三类生态组合(即: No. 1, No. 2和No. 3), 代表前滨—近岸—远岸的沉积环境。其中, 近岸环境的枝状—双叶状—网状苔藓虫组合的属种丰度、分异度最高。     

Evaluation of malacosporean life cycles through transmission studies

Myxozoans, belonging to the recently described Class Malacosporea, parasitise freshwater bryozoans during at least part of their life cycle, but no complete malacosporean life cycle is known to date. One of the 2 described malacosporeans is Tetracapsuloides bryosalmonae, the causative agent of salmonid proliferative kidney disease. The other is Buddenbrockia plumatellae, so far only found in freshwater bryozoans. Our investigations evaluated malacosporean life cycles, focusing on transmission from fish to bryozoan and from bryozoan to bryozoan. We exposed bryozoans to possible infection from: stages of T. bryosalmonae in fish kidney and released in fish urine; spores of T. bryosalmonae that had developed in bryozoan hosts; and spores and sac stages of B. plumatellae that had developed in bryozoans. Infections were never observed by microscopic examination of post-exposure, cultured bryozoans and none were detected by PCR after culture. Our consistent negative results are compelling: trials incorporated a broad range of parasite stages and potential hosts, and failure of transmission across trials cannot be ascribed to low spore concentrations or immature infective stages. The absence of evidence for bryozoan to bryozoan transmissions for both malacosporeans strongly indicates that such transmission is precluded in malacosporean life cycles. Overall, our results imply that there may be another malacosporean host which remains unidentified, although transmission from fish to bryozoans requires further investigation. However, the highly clonal life history of freshwater bryozoans is likely to allow both long-term persistence and spread of infection within bryozoan populations, precluding the requirement for regular transmission from an alternate host.     

Colony Structure and Seasonal Differences in Light and Nitrogen Modify the Impact of Sessile Epifauna on the Giant Kelp Macrocystis pyrifera (L.) C Agardh

The presence of the stoloniferous hydroid Obelia geniculata (L.) had no effect on the pigment concentration or nitrogen status of underlying blade tissue of the giant kelp Macrocystis pyrifera (L.) C. Agardh. The sheet-like colonies of the bryozoan Membranipora membranacea (L.) markedly reduced the pigment concentration of colonized blade tissue, but only during winter. Reductions in pigment concentration are most likely a result of damage to underlying tissue due to some factor related to the presence of bryozoan colonies on blade surfaces. Blade tissue colonized by M. membranacea also had higher δ¹⁵N signatures than surrounding bryozoan-free tissue, possibly indicating the provision of nitrogen to M. pyrifera by bryozoan colonies. Results show that seasonal changes in nitrogen and colony size can strongly modify the effect of epifauna on macroalgae they colonize. Unlike bryozoans, hydroid colonies provided no barrier to nitrogen uptake by colonized M. pyrifera tissue and enhanced ammonium uptake was observed for tissue colonized by O. geniculata during nitrogen limitation. Epifauna with stoloniferous growth forms such as hydroids are more likely to have benign or even mutualistic relationships with macroalgae they colonize than the sheet-like colonies of bryozoans.     

Long-term variability in the abundance of Antarctic fur seals Arctocephalus gazella at Signy Island, South Orkneys

The number of Antarctic fur seals Arctocephalus gazella hauled out at Signy Island in the South Orkneys was monitored annually between 1977 and 2008. Over the study period seal abundance showed a tenfold increase, from a minimum of 1,643 seals in 1978 to a maximum of 21,303 in 1994. The majority of individuals observed were young adult males, likely to be migrants from South Georgia, with small numbers of female seals and only 65 pups recorded during the survey period. Variability in counts showed a similar pattern to Laurie Island, also in the South Orkneys archipelago, suggesting a similar annual immigration of seals to these two islands. The date of first seal arrival was correlated with the date of fast-ice breakout at Factory Cove, Signy Island, and years in which break out was exceptionally late (>21 December) corresponded with years of reduced seal abundance. While the presence of fast-ice during the early breeding season may currently inhibit the establishment of a major breeding population of fur seals at Signy Island, it is important that routine monitoring should continue, particularly in the light of current patterns of climate warming in the Antarctic.     

Bryozoans are returning home: recolonization of freshwater ecosystems inferred from phylogenetic relationships

Bryozoans are aquatic invertebrates that inhabit all types of aquatic ecosystems. They are small animals that form large colonies by asexual budding. Colonies can reach the size of several tens of centimeters, while individual units within a colony are the size of a few millimeters. Each individual within a colony works as a separate zooid and is genetically identical to each other individual within the same colony. Most freshwater species of bryozoans belong to the Phylactolaemata class, while several species that tolerate brackish water belong to the Gymnolaemata class. Tissue samples for this study were collected in the rivers of Adriatic and Danube basin and in the wetland areas in the continental part of Croatia (Europe). Freshwater and brackish taxons of bryozoans were genetically analyzed for the purpose of creating phylogenetic relationships between freshwater and brackish taxons of the Phylactolaemata and Gymnolaemata classes and determining the role of brackish species in colonizing freshwater and marine ecosystems. Phylogenetic relationships inferred on the genes for 18S rRNA, 28S rRNA, COI, and ITS2 region confirmed Phylactolaemata bryozoans as radix bryozoan group. Phylogenetic analysis proved Phylactolaemata bryozoan's close relations with taxons from Phoronida phylum as well as the separation of the Lophopodidae family from other families within the Plumatellida genus. Comparative analysis of existing knowledge about the phylogeny of bryozoans and the expansion of known evolutionary hypotheses is proposed with the model of settlement of marine and freshwater ecosystems by the bryozoans group during their evolutionary past. In this case study, brackish bryozoan taxons represent a link for this ecological phylogenetic hypothesis. Comparison of brackish bryozoan species Lophopus crystallinus and Conopeum seurati confirmed a dual colonization of freshwater ecosystems throughout evolution of this group of animals.     

Infection of bryozoans by Tetracapsuloides bryosalmonae at sites endemic for salmonid proliferative kidney disease

Laboratory-reared colonies of the bryozoans Fredericella sultana and Plumatella fungosa were placed upstream of 2 fish farms endemic for salmonid proliferative kidney disease (PKD) to assess rates of infection of bryozoans by Tetracapsuloides bryosalmonae, the causative agent of PKD. Colonies were deployed in the field for 8 trial periods of 2 wk each throughout the summer of 2001. Following each trial, bryozoan colonies were maintained in laboratory culture for 28 d and were regularly monitored for infection by searching for sac stages of T. bryosalmonae. Infections were never identified by observations of sac stages, however positive PCR results and sequencing of cultured material confirmed that cryptic infections were present in colonies of both species deployed at one site. The possibility that PCR results reflected contamination of surfaces of bryozoans can be excluded, given the short period of spore viability of T. bryosalmonae. Highest rates of infection occurred when 4 of 23 colonies of F. sultana and 1 of 12 colonies of P. fungosa were infected during the period 10 to 24 July. No infections were detected from mid-August to late October at this site. None of the colonies at the other site became infected throughout the period of study. Our data provide the first estimates of infection rates of bryozoans by T. bryosalmonae. Additionally, they provide evidence that a cryptic stage can be maintained within bryozoan hosts for a period of 4 to 6 wk.     

Epizoic bryozoans and corals as indicators of life and post-mortem orientations of the Devonian brachiopod Meristella

The in-life and post-mortem orientations of the Lower Devonian brachiopod Meristella atoka from the Haragan Formation (Lower Devonian; south-central Oklahoma) are inferred from the distribution of epizoic bryozoans and the orientations of base plates of epizoic corals. Three bryozoans, Cyphotrypa corrugata, Fistuliporella maynardi and Leioclema pulchellum, and one coral, Favosites conicus, are considered. Most zoaria that contact the commissure terminate at the commissurc, and a few zoaria terminate at growth lines. This suggests that the bryozoans were primarily life associates of Meristella atoka. Collectively, these three bryozoan species most extensively encrusted marginal sectors of the brachial valve and are very rare on the posteromedian sector (the umbo) of the pedicle valve. This distributional pattern indicates that the preferred living orientation of Meristella atoka was umbo-down (posteromedian sector of the pedicle valve resting on or buried in the substratum) with the commissure steeply inclined to the sediment water interface. Most coralla of Favosites conicus that contacted the commissure encrusted over the commissure. This indicates that Favosites conicus either preferentially encrusted Meristella atoka post-mortem or colonized living brachiopods but subsequently caused them to die. Furthermore, Favosites conicus most extensively encrusted anterior sectors of the brachial valve, especially the fold. The lateral and anterior orientations of the commissure with respect to the base plates (holothecae) of Favosites conicus indicates that the brachiopods were oriented approximately horizontal with respect to the base plates. This suggests that the preferred post-mortem orientation of Meristella atoka was resting nearly horizontally on the substratum. These data and interpretations confirm previously inferred in-life orientations of Meristella atoka and are consistent with post-mortem orientations hypothesized for elongate-oval athyrid brachiopods. □Brachiopoda, Athyridacea, Meristella atoka , palaeoecology, autecology, epizoans, bryozoans, corals, sedimentology, Lower Devonian, North America, Oklahoma.     

Niche relations in a small world: Epizoic algae on an intertidal gastropod

The patterns of microhabitat use were investigated in three coexisting epizoic algae on an intertidal gastropod, Lunella correensis in an attempt to enhance understanding of the niche relations among ecologically similar species in a space-limited environment. Our analysis of field-derived data showed clear spatiotemporal partitioning of shell microhabitats by epizoic algae with different degrees of resource specialization. As a substrate-specializing, obligate epizoic alga, Pseudocladophora conchopheria occupied wider micro-niches on the host of different sizes than facultative epizoic algae (encrusting rhodophytes, crustose Corallina and Gelidium). While Pseudocladophora demonstrated uniform use of all shell microhabitats on hosts of all sizes, crustose Corallina and Gelidium showed more varied microhabitat use with shifting positions on hosts of different sizes. Furthermore, in addition to slight differences in microhabitat use, crustose Corallina and Gelidium demonstrated differences in their interspecific relationship with Pseudocladophora. Our generalized linear models (GLM) analyses indicated that the occurrence/abundance of crustose Corallina was negatively affected by Pseudocladophora but that of Gelidium was positively affected, while Pseudocladophora appeared to be competitively inferior to both rhodophytes when they co-occurred on hosts of relatively large sizes. The present study, therefore, points to variable niche partitioning among algae even on a small spatial scale, which may result from complex interactions between spatio-temporal substrate heterogeneity on a live host and interspecific interactions.     

The effects of infection by Tetracapsuloides bryosalmonae (Myxozoa) and temperature on Fredericella sultana (Bryozoa)

The myxozoan, Tetracapsuloides bryosalmonae, exploits freshwater bryozoans as definitive hosts, occurring as cryptic stages in bryozoan colonies during covert infections and as spore-forming sacs during overt infections. Spores released from sacs are infective to salmonid fish, causing the devastating Proliferative Kidney Disease (PKD). We undertook laboratory studies using mesocosm systems running at 10, 14 and 20 °C to determine how infection by T. bryosalmonae and water temperature influence fitness of one of its most important bryozoan hosts, Fredericella sultana, over a period of 4 weeks. The effects of infection were context-dependent and often undetectable. Covert infections appear to pose very low energetic costs. Thus, we found that growth of covertly infected F. sultana colonies was similar to that of uninfected colonies regardless of temperature, as was the propensity to produce dormant resting stages (statoblasts). Production of statoblasts, however, was associated with decreased growth. Overt infections imposed greater effects on correlates of host fitness by: (i) reducing growth rates at the two higher temperatures; (ii) increasing mortality rates at the highest temperature; (iii) inhibiting statoblast production. Our results indicate that parasitism should have a relatively small effect on host fitness in the field as the negative effects of infection were mainly expressed in environmentally extreme conditions (20 °C for 4 weeks). The generally low virulence of T. bryosalmonae is similar to that recently demonstrated for another myxozoan endoparasite of freshwater bryozoans. The unique opportunity for extensive vertical transmission in these colonial invertebrate hosts couples the reproductive interests of host and parasite and may well give rise to the low virulence that characterises these systems. Our study implies that climate change can be expected to exacerbate PKD outbreaks and increase the geographic range of PKD as a result of the combined responses of T. bryosalmonae and its bryozoan hosts to higher temperatures.     

Seasonality of feeding activity in Antarctic suspension feeders

The feeding activity of four benthic suspension-feeding groups (bryozoans, hydroids, polychaetes and holothurians) was monitored in situ every month for a 2-year period at Signy Island in the maritime Antarctic. The bryozoans were monitored at species level, whereas the other taxa could be differentiated only to genus. A marked seasonal variation in feeding activity was observed in most taxa. Although environmental parameters such as sea water temperature, fastice duration and water column chlorophyll concentrations suggested that winter in the maritime Antarctic lasts for about 6 months, many animals ceased feeding only for a short period of 2 or 3 months around the middle of the austral winter (June/July). These suspension feeders must therefore be efficient at utilising the low concentration of the microplankton existing in the water column for much of the year. Comparison with environmental variables suggested several possible cues for changes in feeding activity, but these cues may differ between taxa. Photoperiod and changes in disturbance by water movement (both mediated by ice), and food concentration are likely to be important environmental cues for polar suspension feeders.     

Composition of bryozoan assemblages related to depth in Svalbard fjords and sounds

Svalbard bryozoan communities were investigated along a depth range from the surface to 296 m between the inner glacial fronts and fjord mouths during 2001 and 2002. The main study area was Kongsfjorden (79°N, 12°E). A total of 137 taxa of bryozoans were identified: 108 to species, 24 to genus, 3 to family, 1 to order and 1 to phylum level. Cluster and multidimensional scaling analyses revealed four distinct assemblages of bryozoans: shallow (0–40 m; 68 taxa), deep (40–296 m; 80 taxa), inner fjordic (three taxa) and an assemblage found on small stones in shallow waters (nine taxa). The inner fjordic assemblage was recorded from the front of tidal glaciers extending about 10 km out into the fjord. In terms of abundance, Celleporella hyalina Linnaeus dominated in shallow areas (18%), Hippothoa arctica Kluge (55%) in deep water, Alcyonidium disciforme Smitt (86%) proximate to glaciers fronts and Electra arctica Borg on small stones (98%). The species were classified according to their depth range as a stenobathic-shallow (46 taxa), stenobathic-deep (57 taxa) and eurybathic-generalist (21 taxa). Mean diversity measures did not show any significant differences between the shallow and deep communities. The bryozoan assemblages seem to be structured primarily by processes related to depth and sediment characteristics.     

Larger foraminifera as a substratum for encrusting bryozoans (Late Oligocene,Tethyan Seaway,Iran)

Considering the diversity and abundance of larger foraminifera examined from a wide range of Late Oligocene to Early Miocene palaeoenvironments in the Tethyan Seaway, encrusting bryozoans make extremely little use of their tests as substratum. Significant encrustations by bryozoans were exclusively found on large (ø c. 6 cm), undulating tests of Lepidocyclina spp., on which, however, a remarkable 34 taxa of encrusting bryozoans were recorded. This shallow-water fauna of Chattian age was analyzed in respect of the bryozoan taxa present, colony growth type, and mode of budding, colony size, as well as onset of reproduction. Taxic and morphological similarities between the fossil assemblage and modern faunas encrusting mobile substrata indicate a long history of bryozoans as part of the interstitial habitat, while the tests of certain larger foraminifera may have played a significant role in the evolution of shallow-water bryozoans by providing substrata for encrusting species in otherwise unfavorable environments.     

Systematics and Biogeography of Burrowing Bryozoans

Current investigations of the three principal families of ectoproctbryozoan burrowers has shown that while two of the families,the Terebriporidae and the Immergentiidae, belong to the minorOrder Ctenostomata, the third family, Penetrantiidae, previouslyconsidered a ctenostome, actually belongs to the major OrderCheilostomata. The implications of this are important; we haveconsidered the burrowing bryozoans to be a small obscure group,specialized for the burrowing mode of existence. We must nowconsider the possibility that there may be many more speciesof burrowing bryozoans as yet undiscovered, that they occurin at least two of the three bryozoan orders, and that burrowingconstitutes an important ecological niche or mode of adaptationfor the bryozoans. While such a change may seem to be merelya taxonomic maneuver, itmay also serve to emphasize the diversityof the ectoproct bryozoan groups which do burrow, and perhapsencourage research on them. At present we are making progressdescribing the living species, their anatomy and histology.We still know almost nothing about how they penetrate the substrate,nothing about possible effects upon the host organism, and nothingabout their means of geographical distribution, although theyseem to occur worldwide, burrowing primarily in molluscan shells.     

Symbiosis of cornulitids with the cystoporate bryozoan Fistulipora in the Pridoli of Saaremaa,Estonia

Cornulites sp. and Fistulipora przhidolensis formed a symbiotic association in the Pridoli (latest Silurian) of Saaremaa Island, Estonia. This Cornulites sp.–F. przhidolensis association is the youngest example of cornulitid–bryozoan symbiosis. Symbiosis is indicated by intergrowth of both organisms. The cornulitids are completely embedded within the cystoporate bryozoan colony, leaving only their apertures free on the growth surface of bryozoan. In terms of food competition, this association could have been slightly harmful to F. przhidolensis as Cornulites sp. may have been a kleptoparasite. There may have been a small escalation in the evolution of the endobiotic life mode of cornulitids as the number of such associations increased from the Ordovician to Silurian. It is likely that Palaeozoic bryozoan symbiosis reached its maximum in the Late Ordovician. Most of the symbiotic bryozoans in the Palaeozoic are trepostomes, and the diversity of symbiotic associations was also greatest among trepostomes.     

Evolutionary palaeoecology of symbioses between bryozoans and hermit crabs

Modern hermit crabs form associations with many organisms which encrust, bore into, or cohabit the living chambers of gastropod shells occupied by the crabs. Among these hermit crab symbionts are bryozoan species which develop massive, commonly multilayered, colonies encrusting hermit crab shells. These colonies extend the living chamber of the crab through a characteristic process of helicospiral tubular growth originating from the shell aperture. The scant information available on the ecology of Recent bryozoan‐hermit crab symbioses is reviewed. Symbioses have been recorded from intertidal to upper slope environments, and from tropical to cold temperate zones. None of the hermit crab species are obligatory symbionts of bryozoans, and the majority of the modern bryozoan species involved are also not obligatory symbionts. Fossil examples always lack the hermit crabs, which have a poor fossilization potential; however, the distinctive tubular growth pattern and other features of the bryozoans enable recognition of ancient examples of the symbiosis. The earliest inferred associations between bryozoans and hermit crabs date from the Mid Jurassic, but associations remained uncommon until the Neogene. A remarkably wide taxonomic diversity of Recent and fossil bryozoans are known or inferred symbionts of hermit crabs. The broad evolutionary pattern of the association demonstrates multiple originations of the symbiosis by bryozoans belonging to at least 5 cyclostome and 12 cheilostome families. Only the Miocene‐Recent cheilostome family Hippoporidridae has an evolutionary history closely tied to symbiosis with hermit crabs. There is no evidence for coevolution.